Flux creep and fishtail in melt-textured and single-crystalline YBa2Cu3O7 |
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Authors: | H Küpfer T Wolf R Kresse R Meier-Hirmer K Salama D Lee and V Selvamanickam |
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Affiliation: | (1) Kernforschungszentrum Karlsruhe, Institut für Technische Physik and Universität Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany;(2) Department of Mechanical Engineering, Texas Center of Superconductivity at University of Houston, 77004 Texas |
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Abstract: | Time-dependent decay of the magnetic moment and magnetization measurements were used to study pinning and flux creep in two samples with and without aj(B) maximum in nonzero field (fishtail effect). From both measurements theE(j) relation was reconstructed forB c and the characteristic current exponent was obtained. At highj and lowB values are between 1 and 4; with increasingB passes a maximum and approaches negative values. At lowj is below 0.5 and not dependent onB orj. This behavior, which is qualitatively the same in both samples, is compared with proposed phase diagrams of the vortex lattice. Large values are correlated with the plateau of the normalized creep rateS 0.025; both observations indicate low relaxation and are found in that lowB region for whichj(B) has its minimum. This observation rejects a dominating influence of relaxation on the fishtail effect. |
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Keywords: | Flux creep J-V curves fishtail |
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